1. Field of the Invention
This invention relates in general to the construction of dry docks and in particular to a new and useful dry dock system or assembly which includes a main dry dock unit of a boxlike construction with one or more pontoons which may be positioned completely below the main dry dock to extend across the whole bottom and which may be ballasted to raise the main dry dock out of the water.
2. Description of the Prior Art
A known dry dock comprises a self docking floating dry dock which comprises a boxlike central or main unit with lifting pontoons which are engageable from below the unit along its entire cross sectional width and which in their lowered self buoyant position are freely displaceable along the central unit. In addition it is known to provide a dry dock which includes an internal subdivision of the lifting pontoon into two flat middle boxes and two L-shaped lateral boxes. In all of the prior art constructions of self docking pontoon docks, the individual pontoons are integrated with the whole structure of the dock with the result that weak points appear in the dock parts which may substantially affect the total strength of the structure. Longitudinal forces occurring during the docking or during the transport on the open sea can be absorbed in the zone of joints and gaps only by the lateral boxes between the pontoon deck and the upper deck which must be substantially reinforced for this purpose. To this end for example reinforcing frames must be provided in the lower chord if the individual pontoons are to be disengageable. In addition the marine insurance companies require a bridging of the gaps between the individual pontoons by means of expensive reinforcements during transportation of the docks on the high seas and these reinforcements must be removed again partly by underwater work after the arrival of the dock at the port of destination or prior to self docking. All docking equipment in every pontoon such as pump shafts, pipings, slide valves, drive shafts, etc. are to be made separable in a suitable manner in order to permit an individual docking of the pontoons.
Special measures must be provided for cross connection cables and supply lines. The connecting lines between the draining installations of the pontoons are to be laid in the lateral box of the central unit and must be equipped with vacuum pumps. The self docking proper is effected step by step. For this purpose the screw connections between the lateral box of the central unit and the pontoons are to be loosened. These operations are frequently difficult because the screw connections are often corroded by the sea water. Extensive repair times in such docks substantially reduce their rentability.